1. Field of the Invention
The present invention relates generally to a treatment device for medical application to body tissue for maintaining antisepsis in long-term indwelling medical devices and, more particularly, it relates to a treatment device which electrolytically infuses silver ions from the surface of an indwelling device into the surrounding tissues under remote control and power delivery from an external source thereby providing an means of long-term antisepsis which is active and controlled.
2. Description of the Prior Art
There have been attempts in the past to develop hydrophilic or lubricious coatings, thrombo-resistant coatings, antibiotic coatings, and even metallic coatings for long-term indwelling medical devices. These attempts have been in an effort to deal with the pervasive issue of sepsis in indwelling medical devices caused primarily by the surface colonization of biofilms. Biofilms are layers or colonies of bacteria which adhere to a foreign surface and protect themselves with a slime layer rendering the bacteria that breed within the slime thousands of times more resistant to known antibacterial agents.
The hydrophilic and lubricious coatings seek to stop the adhering of these films and thus thwart the development of the colonies. The thrombo-resistant coatings seek to resist the protein layer build-ups that can host the colonies. The metallic coatings and antibiotic coatings seek to kill the bacteria as they attach. Unfortunately, the coatings have quite clearly failed for various reasons to provide sufficient protection by any of those means. Sepsis of indwelling devices (catheters, ports, prosthetic joints, meshes, and shunts) still range from 5% to 15%.
The failure of these techniques rests in part on the fact that these techniques are all passive. That is to say, the techniques do not force interaction between the surface and the bacteria. A silver coated surface elutes too slowly to repel or effectively inhibit the colonizing bacteria. While special silver coatings have been developed which have high rates of elution, the silver coatings exhaust their capability frivolously in a few days by continuously eluting at rates that cannot be sustained. Antibiotic coatings effectively kill the layer of colonizing bacteria that adhere to the surface. Ironically, this activity is its own un-doing as the dead bacteria serve as an insulating layer to protect and facilitate adherence of the next layer. None of the existing systems offer any means for effectively penetrating the biofilm layer that protects the bacterial colonies and hence offers extremely limited effectivity.
Additionally, since the release of agent from these existing technologies is dependant upon the interstitial environment, the dose over time changes in some unknown manner varying with the person, with time, and with the adherence of proteins. As a fibrin sheath builds up on the surface and the material elutes in rates determined by the physiology of the particular surrounding tissue and individual, the actual dose, rate, and effectiveness diminish and become unknown. This renders the present techniques quite ineffective and difficult or impossible to clinically verify.
The present invention is a device for maintaining antisepsis of tissue of a body. The device comprises at least a first active surface contactable with the tissue and at least a second active surface contactable with the tissue. A control system is electrically connected to the first active surface and the second active surface with the control system creating an electric field between the first active surface and the second active surface through the body. Silver, an antimicrobial substance, is on or comprised of at least a portion of the first active surface with the substance being ionized upon application of the electric field thereby profusing the substance into the tissue.
In yet another embodiment of the present invention, the device further comprises using a bipolar field at low frequencies allowing both the first active surface and the second active surface to act as anodes. Preferably, the device further comprises using a bipolar field at low frequencies to maintain a surface only distribution of the substance.
In still another embodiment of the present invention, the method further comprises providing an embedded microcontroller or other control circuitry for controlling the delivery rate of the substance, dose of the substance, and selected active surfaces.
In these embodiments, the therapeutic protocol administered by the embedded microcontroller is controller by embedded firmware within the implanted device. Alternately, the therapeutic protocol is modified or communicated entirely through the modulation of the applied electromagnetic signal. The electromagnetic signal serves to allow communication to the embedded microcontroller, which is controlling the administration of silver ions, and to provide power for the operation of the system. This is accomplished by modulating the RF electromagnetic field, which is being applied to the system transcutaneously. The modulation of the applied field is detected by the circuitry of the system and then de-coded by the microcontroller. The modulation could be amplitude based, frequency shift keying based, phase shift keying or any other modulation technique known to one skilled in the art.
The system of the present invention derives power from this applied RF electromagnetic field, an internal battery, or any other power source. The system then generates the higher voltages necessary to force the ionization of silver from the active surface surfaces and the penetration into the surrounding tissue or biofilms by means of a controllable DC-to-DC converter. The converter is operated by the embedded microcontroller and can be adjusted in real-time to produce the required waveforms.
In the case of a battery operated system, the system is pre-programmed to come out of a stand-by mode (wake-up) and operate, treating the surrounding tissue according to the protocol required for the particular application. After treatment (typically five (5) to fifteen (15) minutes) the system goes back to sleep (stand-by) thus conserving battery power and surface silver until it is required to operate again. This can be daily, or weekly depending on the expected re-colonization rate of the device.